The invention relates to optical disk data reproduction, in particular to regenerating data signals that have been recorded based on a duo-binary (1+D) partial response characteristic.
DVDs (digital versatile disc) have currently the highest storage density among the optical discs of practical use. Due to the high storage density the reproduced signal is deteriorated by noise caused by inter-symbol interference, crosstalk, focus error, mastering errors.
It is a well-known fact that the signal-to-noise ratio SNR influences the detecting performance of a bit detector. A conventional bit detector, for example a threshold detector, generates a high bit error rate in case of low SNR.
For accurate reproduction of digital data from a DVD under low SNR conditions, a Viterbi detector or Viterbi algorithm can be used which performs maximum likelihood sequence estimation MLSE.
MSLE and Viterbi algorithms are disclosed in e.g.:
xe2x80x9cThe Viterbi Algorithmxe2x80x9d, G. D. Forner, Proceedings of IEEE, Vol. 61, No. 3, March 1973, pp. 268-278;
xe2x80x9cMaximum-Likelihood Sequence Estimation of Digital Sequences in the Presence of Intersymbol Interferencexe2x80x9d, G. D. Forner, IEEE Transactions on Information Theory, Vol. 18, No. 3, May 1972, pp. 363-378.
Applications of MLSE or Viterbi algorithms with a partial response (PR) system are disclosed in e.g.:
xe2x80x9cA PRML System for Digital Magnetic Recordingxe2x80x9d, R. D. Cideciyan, F. Dolivo, R. Hermann, W. Hirt, W. Schott, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, Vol. 10, No. 1, January 1992, pp. 38-56;
xe2x80x9cViterbi Detection of Class IV Partial Response on a Magnetic Recording Channelxe2x80x9d, R. W. WOOD, D. A. Petersen, IEEE Transactions on Communications, Vol. COM-34, No. 5, May 1986, pp. 454-461;
xe2x80x9cVariations on the FERGUSON Viterbi Detectorxe2x80x9d, J. W. M. Bergmans, K. D. Fisher, H. W. Wong-Lam, Philips Journal of Research, Vol. 47, No. 6, 1993, pp. 361-386;
xe2x80x9cOptimal reception for binary partial response channelsxe2x80x9d, M. J. Ferguson, Bell Systems, Technical Journal 51 (2), 1972, pp. 410-30;
xe2x80x9cA study of digital auto equalizer and PLL system using Maximum Likelihood Error for digital VCRsxe2x80x9d, J. Tonami, T. Kiyofuji, A. Suyama, IEEE Transactions on Consumer Electronics, Vol. 43, No. 3, August 1997;
xe2x80x9cNew Feedback Viterbi Decoder for digital VCRsxe2x80x9d, S. Kitaori, IEEE Transactions on Consumer Electronics, Vol. 41, No. 3, August 1995;
xe2x80x9cOn the application of sequence estimation algorithms in the Digital Compact Cassette (DCC)xe2x80x9d, V. Braun, K. A. Schouhamer Immink, M. A. Ribeiro, G. J. van den Enden, IEEE Transactions on Consumer Electronics, Vol. 40, No. 4, November 1994.
Applications of Viterbi detectors are described in EP-A-0 644 661, U.S. Pat. No. 5,392,316, and U.S. Pat. No. 4,571,734.
The above mentioned documents concern the application of a Viterbi Detector to the class IV partial response on a magnetic recording channel only and are not suitable for an optical recording channel.
xe2x80x9cDVD players using a Viterbi Decoding Circuitxe2x80x9d, H. Hayashi, H. Kobayashi, M. Umezawa, S. Hosaka, H. Hirano, IEEE Transactions on Consumer Electronics, Vol. 44, No. 2, May 1998, discloses Viterbi decoding in a DVD player.
A problem to be solved by the invention is to disclose a method and an apparatus for Viterbi detection, which are suitable for an optical channel with low SNR values.
The recorded data are reconstructed in a special Viterbi detector using a partial response class 1 characteristic, i.e. a (1+D) signalling technique. The signal obtained from the recording signal has three values corresponding to e.g. xe2x88x922,0, +2, respectively. The Viterbi detector treats a sequence of such signals. When the maximum likelihood (ML) data is detected, the ML data transition path leading to the detected data is searched and the bits on the resulting ML data transition path are assumed to correspond to the originally recorded signal data.
Using the inventive Viterbi detector in the replay section of a DVD player leads to decreased video data output error rate and improves the quality of the correspondingly displayed signal.
In principle, the inventive method is suited for determining the value of samples received from data stored on a storage medium, said data representing a bitstream, and for recovering bits of said bitstream using a Viterbi detector, and includes the following steps:
calculating for the received sample values a corresponding center value, wherein for providing center value calculation input samples from a received original sample value a previously calculated center value is subtracted;
converting said center value calculation input samples by adding a succeeding one to a current one;
calculating, based on said converted center value calculation input samples, branch metric values using a Trellis diagram;
calculating in each case two differential branch metric values from said branch metric values;
calculating a sign value for each of said converted center value calculation input samples;
calculating path metric memory control values using said differential branch metric values and said sign values;
generating the corrected bit values of said bitstream to be recovered using a path metric memory stage, which is controlled by said path metric memory control values.
In principle the inventive apparatus is suited for determining the value of samples received from data stored on a storage medium, said data representing a bitstream, and for recovering bits of said bitstream using a Viterbi detector, and includes:
means for calculating for the received sample values a corresponding center value, wherein for providing center value calculation input samples from a received original sample value a previously calculated center value is subtracted;
means for converting said center value calculation input samples by adding a succeeding one to a current one;
means for calculating, based on said converted center value calculation input samples, branch metric values using a Trellis diagram;
means for calculating in each case two differential branch metric values from said branch metric values;
means for calculating a sign value for each of said converted center value calculation input samples;
means for calculating path metric memory control values using said differential branch metric values and said sign values;
a path metric memory stage for generating the corrected bit values of said bitstream to be recovered, which is controlled by said path metric memory control values.